In the field of chemical process sampling, there has been a long felt need for improved sampling valves. Either single or multiplex valves are needed to sample an ongoing chemical process by receiving gas or liquid and upon control actuation, extract a sample of a process stream to be introduced into a chemical process analyzer such as a gas or liquid chromatograph and after the sample is taken, the valve is closed to the process stream.
In multiplex applications a number of valves are each coupled to a different stream at their input and to a single process analyzer at their output. The valves are actuated at different times to provide sampling of each of the streams without intermixing or cross contamination of samples. At the close of the sampling cycle, any residual of the sample stream is discharged from the actuated valve via a common vent output.
Since the valves must be usable in a variety of industries, sampling of a variety of process streams is expected. It is therefore essential that the valves be chemically resistant and diffusion resistant to the sample streams which they might encounter. More specifically, they must be chemically resistant to material such as strong oxidizers, reducing agents, petrochemicals, especially aromatics and any combinations of such compounds.
Since the valves may be sampling streams from a process which is conducted at elevated or refrigerated temperatures, the valves must operate reliably in a range of the least 0 degrees F. to 300 degrees F.
The valves need to have a high degree of external leak integrity to prevent fire or toxic hazard as well as to minimize what is termed, fugitive emissions.
From the structural standpoint, the valves need to be small in size, simple in design and preferably available for assembly into a variety of modular forms for multiplexing a number of valves together at the input of the single process monitor.
The selection of materials for the valve's structure, as well as its essential seals, must all meet the standard of chemical and diffusion resistance as well as freedom from abrasion or wear which could cause contamination of samples, wear, leaks and shortened operational life. For a truly acceptable valve, some minimum one million cycles of trouble-free operation is needed.
Internally, it is desired that the flow path from the input stream through the valve be as straight or clear is possible, of minimum volume, and without dead end passages which can retain sampled fluid after the sample procedure is completed.
Heretofore, single valves and multiplex valves have been developed but they have failed to meet all of the standards set forth above. Complexity of design, the requirement of numerous seals and presence of confined passage ways have been common. The need for many seals, the failure or abrasion of any one of which may cause leak or contamination of the sample has definitely been the major cause of shortened life of the valves.